The continuously renewing intestinal epithelium is dependent upon a well-regulated system of proliferation and differentiation. As the cells migrate from the proliferative compartment at the crypt base they differentiate. This process becomes disordered in colonic neoplasms. Our objective here is the study of one possible mechanism coordinating these events. The expression of intestine-specific genes requires the caudal-related genes, Cdx1 and Cdx2. Additionally, several studies suggest Cdx1 and Cdx2 can regulate intestinal cell differentiation and proliferation. Our research has been directed to investigate these effects, and we have developed methods to study them. Our preliminary data will establish that transient expression of Cdx1 in rat intestinal IEC6 cells and human colon cancer DLD1 inhibits proliferation and induces a G0/G1 block. This block was associated with loss of cyclin D1 mRNA and protein expression. We have identified a different system to model Cdx induction of differentiation. Colo 205 colon cancer cells acquired an obvious cell-cell adhesion phenotype with induction of Cdx1 or Cdx2 expression. This was associated with altered cellular morphology including a polarized, columnar shape, apical microvilli, adherens, desmosomal junctions, and tight junctions. This proposal is directed toward characterizing the growth and differentiation effects further and is based on the following hypotheses: (1) Cdxl induces a G0/G1 block by a down-regulation of cyclin D1 gene expression, and (2) Cdxl or Cdx2 expression promotes morphologic maturation by inducing cell-cell adhesive interactions and activating novel Cdx transcriptional targets. The Specific Aims of this proposal are (1) to examine the effects of Cdx1 or Cd2 on the proliferation of human colon cancer cells; (2) to study the role of cyclin D1 in Cdx1 growth inhibition; (3) to characterize the effects of Cdxl on a-catenin and E2F transcriptional activity; and, (4) to determine the effects of Cdxl or Cdx2 on human Colo 205 differentiation and cell-cell adhesion. This proposal explores a role for the Cdx factors in regulating the processes of cell-cell adhesion, morphologic maturation, and proliferation of the intestinal cell. Understanding these mechanisms will improve our knowledge of normal events in the colonic crypts as well as the dysregulation of differentiation and proliferation found in human colon cancers.